At the current rate of usage, there is estimated to be about 300 years of coal deposits left in mines across the U.S.A. Coal is a valuable natural resource that represents one of the most abundant and efficient sources of energy available in the U.S. today. At the same time, there are also serious environmental hazards and consequences associated with the use of coal, including the emission of carbon dioxide gas which can lead to global warming and other climate changes.
Greenhouse gases are found in the earth's atmosphere and contribute to the greenhouse effect. In the absence of the greenhouse effect, the mean temperature of the earth could be reduced to about minus 19 degrees C. (or minus 2 degrees F.) rather than the present mean temperature of about 15 degrees C. (or 59 degrees F.), thereby making the earth uninhabitable. On the other hand, with an increase in greenhouse gases, the earth could experience the opposite effect—global warming.
Greenhouse gases include in the order of relative abundance water vapor, carbon dioxide, methane, nitrous oxide, and ozone, among others. The majority of these green house gases exist in nature, but the extent to which any one particular gas, such as carbon dioxide, is increased can change due to human activity.
Of the major greenhouse gases existing on the earth today, water vapor is estimated to cause about 36-70% of the overall greenhouse effect (not including clouds); carbon dioxide is estimated to cause about 9-26%; methane is estimated to cause about 4-9%, and ozone is estimated to cause about 3-7%. It is not possible to determine the exact percentage of the greenhouse effect caused by any one gas because the influences of the various gases are not additive. For example, the higher end of the ranges are for one gas alone, whereas, the lower ends are for the gases including overlaps. Other greenhouse gases include, but are not limited to, nitrous oxide, sulfur hexafluoride, hydrofluorocarbons, perfluorocarbons and chlorofluorocarbons.
One of the main contributors to global warming is believed to be the increase in carbon dioxide gas emitted into the earth's atmosphere by various man-made activities and technologies. Of the main contributors to carbon dioxide emissions that can affect the earth's atmosphere and therefore increase global warming, the top seven are listed below (with percentage contributions for 2000-2004):                1. Solid fuels (e.g. coal): 35%        2. Liquid fuels (e.g. gasoline): 36%        3. Gaseous fuels (e.g. natural gas): 20%        4. Flaring gas industrially and at wells: <1%        5. Cement production: 3%        6. Non-fuel hydrocarbons: <1%        7. The “international bunkers” of shipping and air transport not included in national inventories: 4%        
While there is a strong motivation to use coal for the generation of energy due to its efficiency and abundance, there is also a strong interest in eliminating the undesired emissions of carbon dioxide gas into the atmosphere created by the combustion of coal in standard coal combustion power plants.
One of the existing technologies used to eliminate excess carbon dioxide emissions involves “capturing” the CO2 as it is being emitted from smokestacks, wherein the intent is to store the carbon dioxide in various locations, including underground reservoirs, oceans, rocks, consumer products, chemicals or fuels. The idea of carbon capture and storage (CCS)—first introduced in the 1970's—began by making use of existing underground reservoirs in which to store the CO2 gas. In this respect, it may be worth mentioning that there are many natural reservoirs of CO2 that have been in existence and contained the gas for millions of years. Moreover, the available storage space in underground reservoirs (such as depleted oil and gas reserves, coal formations and saline formations) is probably large enough to store all the carbon dioxide gas contained in all the remaining fossil fuel reserves.
Recently, leading science and energy institutes advocated strongly for the further development of carbon capture and storage technology. For example, in June of 2008, the science academies of the world's 13 major economic powers called the implementation of carbon sequestration a “top priority.” At about the same time, the International Energy Association (IEA) argued for an energy technology revolution of which carbon capture and storage is to form a vital component. Meanwhile, many spin-offs and start-ups are presenting various “innovative” ideas that differ from the traditional approach of storing CO2 in underground caverns and reservoirs.
For example, capturing CO2 from smokestacks for the purification of natural gas or at ammonia production facilities has been a common practice for many years. Moreover, injection and storage of carbon dioxide is already occurring in the North Sea, Algeria, and Texas, and in these cases, CO2 is being injected into oil and gas reservoirs, which provides the added benefit of being able to extract more fossil fuel than would otherwise be possible using a process called Enhanced Oil Recovery (EOR). And, for some of these applications, carbon dioxide is transported by a pipeline or by ship.
While some of these technologies have gained credibility in recent years, many experts still believe that because of the rapid use of the world's remaining fossil fuel supplies, it is necessary to further lower the environmental impact caused by these technologies in an effort to prevent catastrophic climate changes. The problem at hand, nevertheless, is that the process of capturing, transporting and storing carbon dioxide gas from coal combustion power plants can dramatically raise energy consumption costs and cause serious health and environmental issues and concerns. For example, if the energy used to capture CO2 emissions is derived directly from the fossil fuels themselves, the benefits of the CO2 savings by capture and storage will be offset by the very same energy intensive process. And, if the energy comes from renewable sources, the technology would be rendered unnecessary as it would be much more efficient to generate electricity directly from the renewable source.
Indeed, it has been discovered that capturing CO2 from smokestacks and compressing it for transport can be one of the most energy-intensive parts of the process. According to the International Panel of Climate Change (IPCC), which prepared a comprehensive study three years ago, capturing technology (including compression of the gas for further transport and storage) can raise the energy consumption of a coal combustion power plant by an average of 32 percent.
It is also insufficient to simply place the smokestacks of a coal plant upside down as suitable underground reservoirs do not necessarily lie beneath the world's power stations. A carbon capture and storage infrastructure also requires a transport infrastructure such as those consisting of pipelines (and tankers) that rival the existing oil and gas network. And manufacturing and installing these thousands of miles of pipelines will require a substantial amount of cost and effort. Moreover, it will take not only more research to find out which reservoirs are suitable for storage and which ones aren't, but the injection of CO2 into underground reservoirs and the monitoring of the transport network (today's pipelines are patrolled by plane every two weeks), as well as the transportation of gas by shipping or pipeline, will typically require significant effort and expense.
Capturing carbon dioxide in rocks also requires a mining and transport infrastructure that is comparable to today's coal industry. For example, to fix a ton of CO2, it is estimated that 1.6 to 3.7 tons of rock would be needed. Not only would these rocks have to be mined and transported to coal plants, but the amount of industrial wastes and mining tailings that can be salvaged—for example, fuel ash from coal plants or de-inking ash from the paper industry—are too small to substantially help offset the cost of the mining and transporting that would be required. The process also generates large amounts of waste materials (apart from the carbonised rocks themselves), and for every ton of carbon dioxide stored in rock, 2.87 to 45.18 tons of disposable materials would be created.
Some attempts have been made in the past to store carbon dioxide in unminable coal beds which are potentially large storage reservoirs for the sequestration of anthropogenic CO2. This solution offers the benefit of enhanced methane production, which could potentially offset some of the costs associated with CO2 sequestration. Nevertheless, the results of a careful study of the economic feasibility of such processes now show that injecting flue gas into unminable coal bed seams to recover methane from coal bed methane (CBM) fields is only marginally economical, and will not significantly contribute to the world's carbon dioxide sequestration needs.
Taking all of the above factors into account, it is estimated that Carbon Capture and Storage will probably raise energy consumption in any given application by as much as fifty percent, and therefore, even if all of the CO2 can eventually be separated and stored, such an increase in energy consumption and costs may be too high of a price to pay to keep the environment clean. For all of the above reasons, a new and improved method and apparatus is needed for the capture and storage of CO2 gases emitted from coal combustion power plants, to overcome the high costs and disadvantages associated with current carbon dioxide extraction and removal processes, such that the world's coal reserves can be used without the consequences of adding to man-made global climate changes, and the high cost of producing energy.